A lithium ion secondary battery is widely used as a power source of, for example, a smartphone. Users of the smartphone demand rapid charging capable of charging a battery for a short time. For the rapid charging, large current charging is necessary. The capacity degradation caused by the large current charging is concerned during the course of cycling. In the past, a rapid charging apparatus has been proposed as described in Patent Literature 1 to Patent Literature 4 below.
In Patent Literature 1, in order to solve the problem that cycle characteristics are degraded in a case where charging current is increased and charging is performed under a high temperature atmosphere for the rapid charging, the following processes are repeated. Specifically, constant current charging is performed at a first stage with large current, the charging current is decreased immediately after it reaches prescribed charging voltage, and charging is performed at a second stage with the decreased current.
Patent Literature 2 describes that charging is performed with charging current exceeding the nominal capacity of a lithium ion secondary battery, is performed to half of a maximum charging capacity, and is then performed with rated charging current. As long as the charging is performed to half of the maximum charging capacity, cycle characteristics are not significantly degraded.
Patent Literature 3 describes that, similar to Patent Literature 1, the control is performed such that the charging current is decreased when the measured voltage reaches near the charging voltage prescribed by the secondary battery.
Patent Literature 4 relates to a configuration of a charging apparatus including a combination of a power source control circuit at a first side and a charging control circuit at a second side. In order to downsize the charging apparatus, an object is to control charging voltage and charging current even when the number of parts is reduced from the circuit configuration in the related art. By incorporating different charging control manners into the first side and the second side, it is possible to similarly control the charging before the number of parts is reduced.    [Patent Literature 1] Japanese Patent Application Laid-open No. 7-296853    [Patent Literature 2] Japanese Patent Application Laid-open No. 2002-135990    [Patent Literature 3] Japanese Patent Application Laid-open No. 2013-13258    [Patent Literature 4] Japanese Patent Application Laid-open No. 2013-51819